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9K views 82 replies 12 participants last post by  James560SEC 
#1 ·
Hello.
How would a 91 560 act if ecu was faulty or even disconnected. Specificly when starting cold. Have checked power to cold start injector with noid lamp its good, set lambda at operating temperature to 50% the only other things I haven't done is check the integrity of the fuel accumilator also haven't been able to check fuel pressure. If I can remove the hose from the nipple on the back side of the F/A and plug it, put a clear hose on there and cycle the I/Switch to prime the system and see if any fuel is leaking out of the nipple past the diaphragm would that save me having to check the fuel pressure.
Any and all thoughts on the matter would be welcome. The car is very hard to start in the AM even after cycling the key several times. Once started runs like a top everything normal.
Any and all thoughts on the matter would be welcome.
Thanks.
 
#5 ·
Accumulator.

Does the car stay in high idle or smell rich even if the motor warms up? I would also check the coolant thermoswitch - it is the 4 pin unit

No once started the engine goes into warm up cycle and is ready to drive as normal.

If you mean the injection ECU, mine ran fine once warmed up but until then was like a car with a carb that didnt have choke applied on a cold morning.
Starts for a split second and invariably quits within a seconds but once started runs flawlessly.

HD,
Apart from the F/A and the check valves in both the fuel pumps where else could I be losing residual pressure but, what is confusing to me is; how come cycling the ignition switch is not helping start right away if indeed I'm losing fuel pressure at rest?
I don't know if it's getting too much fuel and not letting it start but depressing the accelerator certainly doesn't help. Waiting five minutes seems to help. Need guidance from you good people.

I really appreciate all of you taking time to address my query. Thank you.
 
#4 ·
... How would a 91 560 act if ecu was faulty or even disconnected. Specificly when starting cold. Have checked power to cold start injector with noid lamp its good ...
If it’s faulty, it depends.

If it’s disconnected and everything else is in order, it depends on the temperature if & how it would start, because the CSV would be deactivated. The CSV receives it’s voltage from the FPR, which receives an edited CTS signal from the CIS-ECU. … If it starts it will run as described by ianrandom, because warm-up & acceleration enrichment via EHA control would not take place.

If it’s disconnected and not everything else is in order, it depends.

... If I can remove the hose from the nipple on the back side of the F/A and plug it, put a clear hose on there and cycle the I/Switch to prime the system and see if any fuel is leaking out of the nipple past the diaphragm would that save me having to check the fuel pressure. ...
No, the fuel accumulator is only one of several possible culprits for loss of holding pressure.

H.D.
 
#8 ·
The ICV was checked at operating temp. to make sure rpm's went up when disconnected tested ok. Engine has no idling problems at any temp.
The fuel filter was replaced a thousand miles ago and no problems before or after installation. This just started suddenly a few weeks ago. After this started happening I changed the FP Relay as I had a known good mercedes brand one from a 1989 560.
If it was carbon build up in the intake plenum or on the inlet valves wouldn't the symptoms show themselves gradually?
With the engine off, cold or hot In a normal operating CIS fuel system when the sensor plate is pushed in a downward direction and released will it spring back to rest position.

Thanks for your response.
 
#9 ·
... If it was carbon build up in the intake plenum or on the inlet valves wouldn't the symptoms show themselves gradually? ...
Certainly.

... With the engine off, cold or hot In a normal operating CIS fuel system when the sensor plate is pushed in a downward direction and released will it spring back to rest position ...
Correct. … But that doesn’t necessarily mean that the control plunger follows the sensor plate’s lever all the way back to its rest possition (on top of the axial seal ring).
 
#12 ·
But before wondering which component might be causing a holding pressure loss, I wonder if there is a holding pressure loss … and suggest to test it.

H.D.[/QUOTE]

So I just went to the car and ran it for a few minuets shut off the engine and then immediately removed the air cleaner cover and pressed down on the sensor plate. The plate returned to its rest position. So, can we say, since the S. Plate did not return to rest position with completely cold engine and it does return shortly after running that it is not a FD problem?
 
#13 ·
... So, can we say, since the S. Plate did not return to rest position with completely cold engine and it does return shortly after running that it is not a FD problem?
The air flow meter plate not returning to its rest position has nothing to do with the FD anyway, no matter whether the engine is cold or warm, or whether the fuel pumps are running or not. … If it doesn’t quickly & freely move back to its rest position and gets stuck somewhere, there’s a mechanical problem with the air flow meter ... which the weak force of the slowly descending control plunger, pushing on the other end of the meter's lever, can not overcome.
 
#15 ·
A test of the fuel system’s holding pressure covers all possible culprits for pressure loss, and is a lot more comfortable to do, IMHO. … On the other hand, if you find out that there is a lack of holding pressure, depending on how quickly the pressure drops, checking the accumulator may than be the next logical step anyway. … So, you decide. :)

H.D.
 
#17 ·
Okay … and if the accumulator is not leaky, and a holding pressure test isn’t very convenient for you, you might first take a closer look at the air flow meter’s & control plunger’s ease of movement when the engine is cold … takes only a few minutes.
 
#24 ·
Hello
So today I checked the system as instructed and the sensor plate was not moving up to its rest position when pushed all the way down. I sprayed intake cleaner continuously with engine running raising RPM as necessary, then switched to a foaming type cleaner/ lubricant in the same manner. Checked again with cold engine as instructed everything checked normal with the sensor plate and control plunger but, there is still pressure loss after about twenty to thirty minutes, which is not acceptable and the engine still has the very same starting problem. I will check the F/ Accumulater first, if that checks good then hopefully I will be able to perform a fuel pressure test tomorrow and take from there.

I was out and about and the engine was hesitating when moving off from a traffic light but, once it reaches full operating temperature there is absolutely no hesitation at all. Sorry I failed to mention that at the beginning of the thread.
Comments would be very welcome.
 
#25 ·
... the engine was hesitating when moving off from a traffic light but, once it reaches full operating temperature there is absolutely no hesitation at all. Sorry I failed to mention that at the beginning of the thread ...
That’s indeed an important piece of information … it indicates a problem either with the CTS, the connection between CTS & ECU, the ECU, the connection between ECU & EHA, or the EHA ... with effect on both cold start and acceleration during the warm-up phase.

Fortunately it’s usually the CTS … I suggest to check its resistance at the disconnected ECU connector when the engine is cold. Your car, presumably not being a California version, should be equipped with a 2-pin CTS in front of the FD. In that case check the resistance between ECU connector terminal 21 & ground. … Btw, disconnect & reconnect the ECU connector always with ignition switched off !

So, in your case there may be a problem with the holding pressure and the CTS signal.

H.D.
 
#26 ·
HD. a hi-jack for gen2 USA with 4 pin CTS, what should the ohms be on the criss/cross pin reading with the key in the nbr 2 position?
 
#28 ·
Gogi that 1 pin is a reading sent to the instrument cluster. The 4 pin in your pic is the reading for the systems of cold start, enrichment, idle control valve, ECU, relay and lambda. It's all considered... and as an edit, the wires are very brittle from the harness.
 
#29 ·
The CTS that has an effect i.a. on cold starts and acceleration during the warm-up phase is either a 2-pin or a 4-pin CTS. In case of a 4-pin CTS its resistance can be checked between the ECU connector terminals 21 & 7.

Here's a list with target values in kΩ:
0°C (32°F): 5.8 – 6.8
5°C (41°F): 4.4 – 5.4
10°C (50°F): 3.6 – 4.3
15°C (59°F): 2.9 – 3.6
20°C (68°F): 2.3 – 2.8
25°C (77°F): 1.9 – 2.3
30°C (86°F): 1.7 – 1.9
35°C (95°F): 1.4 – 1.7
40°C (104°F): 1.1 – 1.4
 
#30 ·
Hd trying to send you a private message. It the box is full. Send me a pm when you create space.
 
#31 ·
Yes, the box was full. Now there’s space for new messages again.

Shouldn’t there be an email notification in a case like this ?

Btw, for quite a while now I also haven’t received email notifications as I used to receive when there was a new post in a thread I participated in.
 
#32 ·
I'm changing the four pin sensor regardless. I removed the connector and checked wiring it looked ok. The wiring did not feel brittle. I don't feel like digging out the ECU to run checks.

So I removed the fuel hose from nipple on the back of the F/ accumulator and plugged it off. After letting the gas drain out of the nipple, I had my friend Cycle the ignition switch three or for times, there was no leakage whatsoever from the diaphragm in the accumulator. Then I performed a fuel pressure test but was unsuccessful as the fitting I had on hand was incorrect and was dripping fuel. With the pumps primed I was seeing 82psi but as soon as th pumps switched off the fuel pressure dropped to zero. I'm not sure if it was all due to the dripping.
So will go to a part store and try to find a bubble fitting to make sure the setup doesn't leak and run another FP test.
Thoughts please. Thanks.
 
#35 ·
I'm changing the four pin sensor regardless. I removed the connector and checked wiring it looked ok. The wiring did not feel brittle. I don't feel like digging out the ECU to run checks ...
The CIS-ECU & the EZL both get input from a double CTS, either a 2-pin or a 4-pin version. In case of a 4-pin CTS one thermistor is interconnected between pins 1 & 3, and the other thermistor is interconnected between pins 2 & 4. By default pins 2 & 4 are connected to the ECU, and pins 1 & 3 are connected to the EZL. But since the pins for each thermistor are positioned diagonally to each other, it actually doesn’t matter how the connector is plugged onto the CTS.

Instead of checking the CTS’s resistance at the ECU connector, you can also measure it directly at the CTS, of course. To check the 4-pin CTS directly, just measure the resistance between pins 1 & 3 and between pins 2 & 4. The target values are the same as listed in post 29.
By measuring the resistance at the ECU or at the EZL, however, the integrity of the connectors and the wires is automatically checked at the same time. … What’s the use of an immaculate sensor if its signal doesn’t reach the unit that processes it?

... checked the accumulator by removing the hose from the nipple, plugging it and energizing the fuel pumps. There was no fuel coming out of the nipple that I had removed the fuel hose from. That means the diaphragm in the accumulator is not ruptured and holding pressure, right? ...
If no fuel was coming out of the nipple on the back side of the accumulator while the fuel pumps ran, it’s holding pressure … at least for 3 seperate seconds. The test would, however, be more realistic with the fuel pumps running for, let’s say, at least 10 consecutive seconds. With the disconnected hose securely blocked and the drain hose securely aiming into a collecting vessel you could bridge the FPR socket with a wire to let the pumps run, or start the engine and see if fuel comes out with the engine running at idle. If then no fuel comes out, you can say that the accumulator is not leaky.

... From what I understand the FPRegulator also holds pressure in the system as well as the check valves in the fuel pumps ...
Neither the fact that no fuel is coming out of the accumulator nipple, nor the fact that there's fuel pressure while the pumps run, means that the fuel pressure regulator and/or the check valves at the pressure port of the fuel pumps are holding the pressure after the pumps are switched off.

The usually underestimated piece of mechanical engineering, that the fuel pressure regulator IMHO is, not only regulates the system pressure (on your car to a range of 90-93 psi) while the fuel pumps run. It also lets the pressure drop to about 50 psi at the moment when the fuel pumps are switched off. These are 2 separate functions of the pressure regulator. It may perfectly ensure the correct system pressure while it can not ensure the correct or any holding pressure anymore.

The check valves are, of course, supposed to open with pressure coming from the pumps, so that there is pressure at the FD. But the question is if they immediately & properly close when the pumps are switched off.

Btw … the quicker the pressure drops to zero as soon as the fuel pumps are switched off, properly connected test equipment provided, the more likely the check valves on both pumps are bad.

H.D.
 
#33 ·
I think it should be holding pressure and IF I read you right, you are losing pressure. Wait for others, but your accumulator seems suspect if I understand you right. The only time you get good pressure is from a hot engine, with consistent fuel flow/demand right.
 
#34 ·
The thing is I checked the accumulator by removing the hose from the nipple, plugging it and energizing the fuel pumps. There was no fuel coming out of the nipple that I had removed the fuel hose from. That means the diaphragm in the accumulator is not ruptured and holding pressure, right?
am I not testing it the right way. From what I understand the FPRegulator also holds pressure in the system as well as the check valves in the fuel pumps.

Any thoughts.
 
#36 ·
The usually underestimated piece of mechanical engineering, that the fuel pressure regulator IMHO is, not only regulates the system pressure (on your car to a range of 90-93 psi) while the fuel pumps run. It also lets the pressure drop to about 50 psi at the moment when the fuel pumps are switched off. These are 2 separate functions of the pressure regulator. It may perfectly ensure the correct system pressure while it can not ensure the correct or any holding pressure anymore.

So are you suggesting that we can rule out the FPR. Also I double checked the sensor plate, with cold engine as per previous instructions ignition off and it stays down when released. If I turn the ignition switch on it instantly pops right back to rest position. When the system is primed and ignition off I can push down on the S. Plate and it will return to rest once or twice before the system loses pressure.

The check valves are, of course, supposed to open with pressure coming from the pumps, so that there is pressure at the FD. But the question is if they immediately & properly close when the pumps are switched off.

Btw … the quicker the pressure drops to zero as soon as the fuel pumps are switched off, properly connected test equipment provided, the more likely the check valves on both pumps are bad.

H.D.[/QUOTE]

I just have a hard time accepting both check valves are bad at the same time.
Could not find the correct fitting to use for the cold start port of the FD that needs to be a bubble fitting. That's where the setup was dripping.

Comments and suggestions please:smile
Kind regards.
 
#43 ·
Yes thanks for pointing that out, I'll keep that in mind. Who knows maybe I will have luck tomorrow and find the correct setup otherwise I can always resort to replacing the least expensive parts first, the check valves but, I do know the fuel pumps were both replaced by the PO.

Thanks.
 
#45 ·
Then that only leaves the accumulator right, I was looking on eBay and I think their about a C note. I'll double check the Accumulator tomorrow just to be sure. I hate throwing parts at a problem without proper diagnosis, it's the only way to go.
 
#50 ·
... could you be more specific about the meter being in series, do you mean check one terminal at a time by bridging the plug to the EHA with the meter in series?
- one measuring cable connected to one of the EHA terminals
- the other measuring cable connected to the corresponding plug terminal
- the other EHA terminal & the corresponding plug terminal bridged with a short cable

And don’t forget: if the meter reads negative amperage with “ignition on” (engine not running), change the polarity of the meter’s measuring cables!
 
#54 ·
Sorry, not up on all the TLA's. When the system is operating excess fuel is returned to the tank. When you shut it off there are places you can have internal leaks that allow pressure to drop and fuel to flow back to the tank.

some shops over new pumps without new check valves.
Unless it's way more complicated/expensive than the SAAB one, sounds like a pretty dumb idea... IIRC it's just a little rubber bit and a spring.
 
#56 ·
... When the system is operating excess fuel is returned to the tank. When you shut it off there are places you can have internal leaks that allow pressure to drop and fuel to flow back to the tank ...
Correct … and these places are the pressure regulator and the accumulator.

As I said in post 35, the pressure regulator keeps the system pressure constant while the fuel pumps run. It leads the always existing excess fuel, no matter in what running condition the engine is, back to the tank.

A separate valve in the pressure regulator lets the pressure drop to the holding pressure when the fuel pumps are switched off. If that valve is leaky, a little fuel (maximum as much as the accumulator holds) flows back to the tank via the same port of the pressure regulator.

The regulator’s valve that keeps the system pressure constant may work perfectly well, while the valve that's supposed to let the system pressure drop to the holding pressure when the pumps are switched off does not work and leaks ... and vice versa.

... Unless it's way more complicated/expensive than the SAAB one, sounds like a pretty dumb idea... IIRC it's just a little rubber bit and a spring.
On MBs it’s a separate, screwed-in, spring loaded ball check valve … well the movable part is not really ball-shaped, but more cone-shaped.

... Ordered check valves.
Okay … however, especially if the check valves look like they were replaced together with the fuel pumps, before I’d replace them I’d check the AFM plate’s zero position & play and the pressure regulator’s, CSV’s and injector’s leak tightness.

H.D.
 
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